A femtocell is a small cellular base station that can be configured to be used indoors, such as within a home or small business, to provide a signal to a mobile device, such as a mobile phone or portable computer with a mobile card or modem. The femtocell is configured to tie into a service provider network broadband connection, such as DSL or cable. The femtocell can be configured to support various numbers of mobile devices; however, current designs usually support 2 to 4 active mobile devices in a residential setting, and 8 to 16 active mobile devices in small business settings (i.e., enterprise setting). A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. The femtocell can be configured for WCDMA, GSM, CDMA2000, TD-SCDMA, WiMAX, and LTE standards.
Femtocells are an alternative way to deliver the benefits of fixed-mobile convergence (FMC). The distinction is that most FMC architectures require a new (e.g., dual-mode) mobile device which works with existing unlicensed spectrum home/enterprise wireless access points, while a femtocell-based deployment will work with existing mobile devices, but requires installation of a femtocell access point that uses licensed spectrum.
Generally, a femtocell provides coverage on the order of 10 s of meters or less, usually about 50 meters to about 30 meters or less. As such, a femtocell environment is typically the size of a residential gateway or smaller, and the femtocell access point connects to a broadband line. Integrated femtocells can include both a DSL router and femtocell. When mobile devices arrive under coverage of the femtocell, they switch over from the macrocell (e.g., outdoor) to the femtocell (e.g., indoor) automatically. All communications then automatically go through the femtocell. When the user leaves the femtocell coverage area, the mobile device hands over seamlessly to the macrocell network. Femtocells require specific hardware, so existing WiFi or DSL routers cannot be upgraded to a femtocell.
Some of the benefits that a femtocell can provide for an end-user include: so-called “5 bar” coverage when there would otherwise be no existing signal or poor coverage; it can provide higher mobile data capacity, which can be important when the end-user makes use of mobile data on their mobile device; and the femtocell can have a functionality and interface that is similar to regular HSPA or LTE base stations, except for a few additional functions with a significantly reduced coverage area.
The placement of a femtocell has a critical effect on the performance of the wider network, and this is a key issue to be addressed for successful deployment. The placement of multiple femtocells in close proximity can impede performance due to the overlap of signal channels, which can cause two femtocells to compete for the same signal channel. Since femtocells can use the same frequency bands, there can be problems with adjacent femtocells interfering with each other to reduce functionality rather than improving functionality.
For example, in order to solve the problems of indoor network coverage, an LTE-A network can incorporate a femtocell, such as a Home Node B (HNB) system or a Home e-Node B (HeNB) system. In this example, a plurality of HeNBs can be densely distributed in a network, which results in the formation of serious interferences between different HeNBs in close proximity. The interference can even cause the nodes in the network to fail to communicate with each other. Uncertainties of the disposition and on-offs of the HeNBs can lead to high randomness of the interferences among the HeNBs.
Attempts have been made to reduce the interference between proximal femtocells. A traditional centralized inter-cell interference coordination technology is limited by its flexibility and transmission delay, and may not rapidly track changes of the interferences between the femtocells. Also, interactions frequently occur among the proximal femtocells, and signaling overhead is high. This can result in the inter-cell interference coordination technology of the traditional cellular network being insufficient for reducing interference between proximal femtocells.